It depends on what the specific'sad Hitler story' is. Some elements might be based on historical facts, like his final days in the bunker which were very desolate. But if it's a more fictionalized account of his emotions or motives, then it may not be strictly based on historical facts.
There's no way to really tell if it's common specifically for someone named Jojo. However, in general, reading fanfiction is a popular activity among fans of many different franchises. The Jojo series has a large and dedicated fan base, so it's likely that there are fans named Jojo who partake in reading fanfiction, but we can't say for sure how common it is without more data.
It didn't conform to historical facts.
Liu Ru was a fictional character from an ancient novel. Her story and character setting had appeared in many novels. Her real name was Hedong Jun, and she was portrayed as a beautiful, intelligent, and talented woman who was once the wife of Feng Bao, a famous Ming Dynasty general who resisted the Qing Dynasty.
Although Liu Rushi's story and character setting appeared in many novels, there was no conclusive evidence of her life and historical records. Therefore, we should not confuse her deeds and characters with the real situation in history.
Perhaps this Jojo is interested in exploring different interpretations and stories within the Jojo universe that fans have come up with. Fanfiction often takes the existing characters, settings, etc. from the original Jojo series and creates new and unique storylines. So, this Jojo might be a big fan of the series and wants to see what other fans have imagined.
It depends. Maybe there are some telltale signs or elements that suggest it's a JoJo reference fanfic, but without specific context, it's hard to say for sure.
The JoJo manga is mainly in black and white. Colored versions exist but are not the norm. Sometimes, colored illustrations are done for promotional purposes or by fans.